1. Field of the Invention
The invention relates to a semiconductor device, particularly, a package type semiconductor device having a light receiving element.
2. Description of the Related Art
Conventionally, a CCD (Charge Coupled Device) sensor, a CMOS (Complementary Metal Oxide Semiconductor) sensor, a sensor for electrically detecting infrared rays (an IR sensor) and so on have been developed as light reading elements. These are elements that convert light into an electric signal.
These device elements are formed on a semiconductor die, and the semiconductor die is sealed in a given structure. FIG. 10 is a cross-sectional view showing a conventional sealing structure schematically.
A device element 101 (e.g. a light receiving element such as a CCD sensor, a CMOS sensor, an infrared ray sensor or the like) and pad electrodes 102 electrically connected to the device element 101 are formed on the front surface of a semiconductor substrate 100 made of silicon or the like.
The semiconductor substrate 100 is attached to a supporting substrate 103 (e.g. a glass epoxy substrate) with an adhesive layer (not shown) being interposed therebetween. Through-holes 104 are formed in the supporting substrate 103, penetrating therethrough from its front surface to its back surface. Lead electrodes 105 made of a conductor such as solder, aluminum or the like are formed in the through-holes 104. The lead electrodes 105 are connected to the pad electrodes 102 through bonding wires 106.
Transparent epoxy resin for sealing 107 is formed over the front surface of the supporting substrate 103, covering all of the semiconductor substrate 100, the bonding wires 106 and so on.
When this semiconductor device is mounted on a packaging substrate (not shown), the lead electrodes 105 on the back side of the supporting substrate 103 are connected to wiring patterns on the packaging substrate.
Recently, the next generation optical disks called the Blu-ray Disk and the HD-DVD (High Definition Digital Versatile Disk) are being developed. When light having a defined wavelength (about 400 to 415 nm) (hereafter, called a blue-violet laser) used for these optical disks impinges on the sealing resin in the above described structure (the epoxy resin 107), the resin is degraded and this degraded resin causes reduction in the operation quality of the semiconductor device (the transmittance of the blue-violet laser or the durability of the semiconductor device). This degradation of the resin has not been taken as a big problem before the above described next generation optical disk is developed.
The resin degradation herein is that the resin is, for example, yellowed, and its transparency is degraded. The resin degradation may occur due to breaking of intermolecular bonds of the resin by a blue-violet laser or heat caused by the blue-violet laser and oxidation of the resin.
For avoiding this problem, the sealing epoxy resin 107 is not formed on the device element 101 in the semiconductor device receiving a blue-violet laser, as shown in FIG. 11. It means that the device element 101 is mounted on the other packaging substrate, being exposed to outside. The relevant technique is described in Japanese Patent Application Publication No. 2005-123553.
In the conventional semiconductor device receiving a blue-violet laser described in FIG. 11, the device element 101 is exposed. Therefore, foreign substances may often adhere to the front surface of the device element 101 during the manufacturing process or in actual use, causing another problem of reduction in the reliability and yield of the device.